President-elect Donald Trump’s transition team early Tuesday announced that he would nominate ExxonMobil CEO Rex Tillerson to serve as his secretary of State.

“His tenacity, broad experience and deep understanding of geopolitics make him an excellent choice for Secretary of State,” Trump said in the announcement. “He will promote regional stability and focus on the core national security interests of the United States.”

Former New Mexico Gov. Gary Johnson is running a third-party presidential candidate as a Libertarian. (Photo By Bill Clark/CQ Roll Call)

Mainstream Republicans are hunting for a third-party candidate to run against presumptive GOP nominee Donald Trump in the general election, a last-ditch effort that could cost Trump votes, but could also pull them away from Democratic front-runner Hillary Clinton.

According to FiveThirtyEight , more than half the electorate has a low opinion of Trump: The percentage of those who have a "strongly unfavorable" opinion of the billionaire businessman was an unprecedented 53 percent in polls taken within the past month. But Clinton's numbers are also unprecedented — while she trails Trump in the “strongly unfavorable” category by double digits, her 37 percent disapproval rating would be the second-highest of any presidential nominee.